The distribution and abundance of the British fungal-breeding Drosophila

Abstract.

• 1 The distribution and abundance of five Drosophila species breeding in fungi are examined by attracting adult flies to baited traps and collecting fungal fruit bodies containing the larval stages.
• 2 Changes in species frequency follow a temporal (seasonal and yearly), rather than a spatial (between and within woods) pattern.
• 3 There is a regular diurnal pattern of activity in D.subobscura but not in D.phalerata. Temperature, light intensity, humidity and wind speed have no effect upon the daily activity of D.phalerata. Only temperature affects the activity of D.subobscura.
• 4 Out of 125 species of fungi collected, only forty-eight species produced Drosophila. However, the flies are even more selective, since only five species of fungi (Phallus impudicus, Polyporus squamosus, Amanita rubescens, Pluteus cervinus and Lactarius quietus) produce 80% of all Drosophila reared.
• 5 The commonest species, D.phalerata, has two or three generations per year with a winter diapause. An outline of the yearly life cycle is given, with the major breeding sites for each generation indicated.
• 6 Measures of niche overlap calculated from the data on individual fruit bodies are very low, suggesting that the five species are effectively isolated during the larval period. This ecological isolation is achieved by a summation of several niche dimensions, woodlands, seasons, fungal species, and individual fruiting body differences.

     

A field study of the association between the stinkhorn Phallus impudicus Pers. and the British fungal-breeding Drosophila

Emergence records for three species of Drosophila breeding in the stinkhorn ( Phallus impudicus ) are presented. These are D. phalerata, D. subobscura and D. cameraria . The numbers of stinkhorn present in one woodland (0.114 km²) have been estimated for a two-year period. In 1976, the total number of these fungal breeding sites during the summer was approximately 8000 and in 1977 it was 5300. Utilizing the estimates of breeding site numbers, Drosophila emergence data and estimates of adult survival from laboratory populations, density estimates for D. phalerata and D. subobscura are calculated.     

A genetic analysis of photoperiodic reproductive diapause in Drosophila triauraria

Abstract. Recombinant inbred lines were produced from hybrids between diapausing and non-diapausing strains of Drosophila triauraria Bock & Wheeler by twenty generations of full-sib mating. The analysis of these inbred lines suggests that the difference in the photoperiodic response between the original diapausing and non-diapausing strains is due to genes at three or four loci and at least one of these loci is located on the X chromosome. The original diapausing strain and two inbred lines exhibited circadian peaks when subjected to the Nanda-Hamner protocol, although they had different critical daylengths. This suggests that critical daylength is modified independently of the circadian oscillation system in this species. On the other hand, diapause duration was correlated with critical daylength among the inbred lines and the original diapausing strain, suggesting that these two traits are under the control of the same genetic system.     

Energy storage during reproductive diapause in the Drosophila melanogaster species group

Summary Temperate species of the Drosophila melanogaster group enter reproductive diapause for overwintering in response to short daylength. During the prediapause period they accumulate triacylglycerols, but not glycogen, as energy resources. The capacity for storing triacylglycerols differs between species, and appears to be closely correlated with diapause and cold-hardiness; cool-temperate species, such as those of the auraria species complex, which enter a deep diapause and are highly cold-hardy, accumulate larger quantities of triacylglycerols than warm-temperate species, such as D. rufa and D. lutescens, which enter a weak diapause and are less cold-hardy. Among the cool-temperate spcies, D. subauraria occurs at a higher latitude and has the greatest capacity for accumulating triacylglycerols. A subtropical species, D. takahashii, which has no diapause in nature and is not cold-hardy, is unable to store the same quantities of triacylglycerols as temperate species.     

Latitudinal clines in the timing and temperature-sensitivity of photoperiodic reproductive diapause in Drosophila montana

Reproductive diapause is a primary mechanism used by arthropods to synchronize their life cycle with seasonal changes in temperate regions. Our study species, Drosophila montana, represents the northern insect species where flies enter reproductive diapause under short day conditions and where the precise timing of diapause is crucial for both survival and offspring production. We have studied clinal variation in the critical day length for female diapause induction (CDL) and their overall susceptibility to enter diapause (diapause incidence), as well as the temperature sensitivity of these traits. The study was performed using multiple strains from four latitudinal clines of the species – short clines in Finland and Alaska and long clines in the Rocky Mountains and the western coast of North America – and from one population in Kamchatka, Russia. CDL showed strong latitudinal clines on both continents, decreasing by one hour per five degrees decline in latitude, on average. CDL also decreased in all populations along with an increase in fly rearing temperature postponing the diapause to later calendar time, the effects of temperature being stronger in southern than in northern population. Female diapause incidence was close to 100% under short day/low temperature conditions in all populations, but decreased below 50% even under short days in 19°C in the southern North American western coast populations and in 22°C in most populations. Comparing a diversity of climatic data for the studied populations showed that while CDL is under a tight photoperiodic regulation linked with latitude, its length depends also on climatic factors determining the growing season length. Overall, the study deepens our understanding of how spatial and environmental parameters affect the seasonal timing of an important biological event, reproductive diapause and helps to estimate the evolutionary potential of insect populations to survive in changing climatic conditions.     

Environmental heterogeneity and the maintenance of genetic variation for reproductive diapause in Drosophila melanogaster

Drosophila melanogaster has colonized temperate habitats on multiple continents over a historical time period, and many traits vary predictably with latitude. Despite considerable attention paid to clinal variation in Drosophila, the mechanisms generating such patterns in nature remain largely unidentified. In D. melanogaster, the expression of reproductive diapause can be induced by exposure to low temperatures and shortened photoperiods. Both diapause expression itself and the underlying genetic variance for diapause expression have widespread impacts on organismal fitness, and diapause incidence exhibits a 60% cline in frequency in the eastern United States. The major aim of this study was to evaluate whether the relative fitness of diapause and nondiapause genotypes varies predictably with environment. In experimental population cages in the laboratory, the frequency of genotypes that express diapause increased over time when flies were exposed to environmental stress, whereas the frequency of nondiapause genotypes increased when flies were cultured under benign control conditions. Other fitness traits correlated with the genetic variance for diapause expression (longevity, mortality rates, stress resistance, lipid content, preadult viability, fecundity profiles, and development time) also diverged between experimental treatments. Similarly, sampling of isofemale lines from natural populations revealed that the frequency of diapause incidence cycled over time in seasonal habitats: diapause expression was at high frequency following the winter season and subsequently declined throughout the summer months. In contrast, diapause expression was low and temporally homogeneous in isofemale line collections from human-associated urban habitats. These data suggest that genetic variation underlying the diapause-nondiapause dichotomy may be actively maintained by selection pressures that vary spatially and temporally in natural populations.     

Aestivo-hibernal reproductive diapause in Drosophila moriwakii: flight as a controlling factor

Drosophila moriwakii Okada & Kurokawa (Diptera; Drosophilidae) generally has only one generation per year and enters aestivo-hibernal reproductive diapause in Sapporo, northern Japan, but a small fraction of the population produced a second generation in summer at a place where breeding resources were abundant. In this species, diapause seems to be controlled by flight activity. When flies were cultured in cages in which they were able to fly freely, they entered diapause irrespective of photoperiod, but they did not do so at long daylengths when cultured in small vials in which they were prevented from flying. Furthermore, flies with wings removed did not enter diapause at long daylengths even if they were cultured in the cages.     

Effects of photoperiodically induced reproductive diapause and cold hardening on the cold tolerance of Drosophila montana

Coping with seasonal and daily variation in environmental conditions requires that organisms are able to adjust their reproduction and stress tolerance according to environmental conditions. Females of Drosophila montana populations have adapted to survive over the dark and cold winters at high latitudes and altitudes by spending this season in photoperiodically controlled reproductive diapause and reproducing only in spring/summer. The present study showed that flies of a northern population of this species are quite tolerant of low temperatures and show high seasonal and short-term plasticity in this trait. Culturing the flies in short day length (nearly all females in reproductive diapause), as well as allowing the flies to get cold hardened before the cold treatment, increased the cold tolerance of both sexes both in chill coma recovery time test and in mortality assay. Chill coma recovery time test performed for the females of two additional D. montana populations cultured in a day length where about half of the females enter diapause, also showed that diapause can increase female cold tolerance even without a change in day length. Direct linkage between diapause and cold tolerance was found in only two strains representing a high-altitude population of the species, but the phenomenon will certainly be worth of studying in northern and southern populations of the species with larger data sets.     

Geographic variation of reproductive diapause in the Drosophila auraria complex (Diptera: Drosophilidae)

ABSTRACT. In the Drosophila auraria complex (D. auraria Peng, D. biauraria Bock & Wheeler, D. triauraria Bock & Wheeler, D. quadraria Bock & Wheeler and D. subauraria Kimura), D. triauraria from the island of Yaku (30.3N in latitude) and D. quadraria from Taiwan (24.1N) had no or weak diapause, while strains of all the four species from the main islands of Japan had a firm reproductive diapause. These strains entered diapause at short daylengths and the critical daylength was longer and the incidence of diapause higher at a low rather than high temperature. In each species, the critical daylength was longer in strains from higher latitudes. Among sympatric populations of different species, D. subauraria always had the longest critical daylength, while D. auraria had the shortest one. The populations of D. biauraria and D. triauraria had longer critical daylengths than the sympatric populations of D. auraria , but this difference became smaller northwards. Since a longer critical daylength induces diapause earlier in autumn, D. subauraria would enter diapause earliest among these species, and D. auraria would do so latest. The late start of diapause in D. auraria may be related to its adaptation to domestic environments. On the other hand, the adaptive significance of the late start of diapause in northern populations of D. biauraria and D. triauraria is not clear.     

Geographic variation and genetic aspects of reproductive diapause in Drosophila triauraria and D. quadraria

ABSTRACT. Geographic variation and genetic aspect of reproductive diapause were studied in Drosophila triauraria Bock & Wheeler and D. quadraria Bock & Wheeler, in relation to their quantitative response to photoperiods. D. quadraria from the subtropical region had no photoperiodic diapause. In D. triauraria strains, diapause was induced under LD 10:14 or 12:12, but not under LD 14:10 or longer photoperiods. Their diapause was induced more effectively and maintained longer by LD 10:14 than by LD 12:12. The duration of diapause was longer in a northern strain, but the diapause inducing process varied little among different geographical strains. Diapause incidence was 50% or lower in F₁ hybrids between D. triauraria and D. quadraria and backcross progenies between F₁ and D. quadraria , and about 70% in backcross progenies between F₁ and D. triauraria under LD 10:14, but very low under LD 12:12. The lower incidence of diapause in these F; and backcross progenies is assumed to be due to the less efficient induction of diapause, since once diapause was induced in them, it was maintained for a long time, especially in the backcross progenies between F₁ and D. triauraria. These experiments suggest that diapause induction and maintenance are different physiological processes controlled by different genetic systems.     

Reproductive biology of British pycnogonids (oögenesis and the reproductive cycle)

There is little information concerning the reproductive biology of the Pycnogonida. Information obtained by the authors concerning the female reproductive system of British pycnogonids is discussed and evaluated.
Oögenesis and vitellogenesis are similar to the processes described in some annelids and crustaceans. Vitellogenesis contrasts with the process in insects where the majority of the yolk is produced extra-oöcytically and is transported to the developing oocyte, whereas in the Pycnogonida the majority of the yolk is produced intra-öocytically with only a small extra-oocyte contribution. This represents a fairly primitive arthropodan type of vitellogenesis.
The reproductive cycles of several British pycnogonid species have been studied by regular sampling at different localities over long periods of time. This has provided information on population dynamics, particularly life-span, migratory movements and fecundity.
Although similarities exist between species there are also marked differences in that some species produce only a single new generation each year, whereas in others the presence of a second population of mature ova in the same year may enable the production of a second brood, if conditions are favourable.     

The influence of temperature and photoperiod on the reproductive diapause and cold tolerance of spotted‐wing drosophila,Drosophila suzukii

Knowledge regarding the reproductive status of spotted‐wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is of critical importance in predicting potential infestations of this invasive pest, as eggs are laid in ripe or ripening fruit of several commercially important small‐fruit crops. Token environmental stimuli for the induction of reproductive diapause and improved cold tolerance were identified for D. suzukii. Diapause induction was evaluated by assessing, via dissection, the number of mature eggs carried by field‐captured D. suzukii and laboratory‐reared D. suzukii held under various temperature and photoperiod regimes. Egg load decreased over time in females trapped from July to December at sites in Benton County, OR, and Ontario County, NY, both USA, and reached zero eggs by December at all sites. Photoperiods below 14 h of day length led to reduced egg maturation in laboratory‐reared flies held at moderate temperatures (15 or 20 °C). Whereas very few mature eggs were found in females held at 10 °C under short‐ or long‐day photoperiods for several weeks after eclosion, a spontaneous return to ovarian maturity was observed in short‐day‐entrained females after 7 weeks. Diapause termination was investigated by evaluating fecundity in diapausing females returned to optimal environmental conditions. Whereas long‐day‐entrained flies began producing offspring immediately upon return to optimal conditions, short‐day‐entrained flies returned after 1 and 6 weeks at 10 °C were slower to produce offspring than colony flies or short‐day‐entrained flies returned after 7 weeks. Cold tolerance was evaluated by observing chill coma recovery rates after 24 h exposure to ?1 °C. Cold‐acclimated (diapausing) females recovered from chill coma faster than cold‐hardened or unacclimated females.     

Reversible reproductive diapause and intermediate states between diapause and full reproductive activity in male Oedipoda miniata grasshoppers

ABSTRACT. Previous publications have shown that aestival reproductive diapause is reversible in Oedipoda miniata (Pall.) males. Short days and/or relatively low temperatures terminate diapause, whereas long days and/or high temperatures maintain or reinduce it. The previous studies proved, however, only the effect of the temperature, or of the daylength—temperature combinations, and employed only male mating behaviour as an indicator of the state of diapause. The present work demonstrates that diapause can be maintained, terminated, or reinduced, solely by changes in the daylength. At a constant 27°C, diapause was terminated under LD 10.5:13.5, whereas it was maintained or reinduced under LD 18:6. The reproductive accessory glands were small in diapausing males and large in post-diapause ones, but their size decreased again with diapause reinduction, thus, they exhibited at least partially reversible changes. An intermediate state between full diapause and full reproductive activity was obtained under intermediate conditions of daylength and temperatures (LD 12:12; photophase (TP) at 38°C, scotophase (TS) at 27°C). In this state males showed consistently mild mating activity and intermediate size of the accessory glands, regardless of whether they had previously been in diapause or in post-diapause states. Under another combination of intermediate conditions (LD 16:8; TP = 26°C, TS = 13°C), another intermediate state with consistently little mating activity was observed. The 'all or none' principle does not apply to this diapause, rather the state of diapause may take any stable intermediate level between full diapause and full reproductive activity. The physiological and ecological implications of these findings are discussed.     

The reproductive biology of Cyclops vicinus

Investigations of the reproductive biology of Cyclops vicinusrevealed that mated females oscillate between gravid and nongravidreproductive conditions. The gravid condition can be dividedin two recognizable phases: gravid/nonovigerous and gravid/ovigerous,the former phase being shortest. The maturation of new oocytestakes place when the old egg sacs are still being carried; thisensures a rapid clutch succession. Females which remain unmated,extrude few eggs, in no case complete egg sacs, and remain gravidthus conserving oocytes. Females which mate only once, showa similar reproductive pattern (clutch size and clutch succession)to those which remain combined with males, and thus have theopportunity to remate, but tend to produce fewer clutches. Malesare able to fertilize 3–4 females day^–1. Matingcapacity of males is possibly limited by the time needed tofill a new spermatophore. Short-term starvation (5 days) lengthenedclutch-to-clutch periods and diminished clutch size. When thestarvation period started in the gravid/ovigerous phase, a normalclutch was extruded but no new oocytes matured during starvation,indicating that the energy for egg maturations is provided inthe first part of the reproductive cycle.     

The reproductive biology of the New Zealand flora

New Zealand's long isolation from other elements of Gondwanaland, oceanic climate, the unusual combination of ancient Gondwanic, tropical and more recently arrived elements in its flora, and its relatively depauperate pollinator and disperser fauna have set the stage for the evolution of a subtle, complex and distinctive reproductive biology. This contrasts markedly with the neighbouring continent of Australia where the fauna is diverse and the flowers vivid. Recent advances in understanding New Zealand's floral biology include evidence that the ancestor to the anthophytes was cosexual, with insect pollinators receiving stigmatic nectar rewards; the discovery of ground-level bat pollination in an obligate root parasite; the finding that the greater resource sensitivity of fruit set in males than in females may account for sex ratio variation in gynodioecious species; and, evidence for much more pronounced mast seeding at higher altitudes even in the absence of mammalian seed predators.     

An investigation of reproductive diapause in two British populations of Anthocoris nemorum (Hemiptera: Anthocoridae)

Certain aspects of reproductive diapause within two British populations of Anthocoris nemorum are investigated and compared.     

The productive and reproductive biology of flowering plants

The life cycles, programme of energy expenditure and allocation to reproduction, and the reproductive efforts of three wildAllium species, i.e.,A. Victorialis ssp.platyphyllum, A. monanthum, andA. Grayi, all native to Japan, were studied and compared. Furthermore, their adaptive strategies were discussed from the point of view of life history strategy. First, the reproductive systems, number of male and female gametes borne, and the number and size of propagules produced were critically investigated. In order to estimate the crude reproductive efficiency (sensu Harper and Ogden, 1970) of these species, sequential harvests were taken and the plants were divided into their component structures, dried and weighed. The quantity of dry weight allocated to sexual or vegetative reproduction was obtained by weighing the seeds, bulbils, or bulblets produced at the end of the season. A. Victorialis ssp.platyphyllum showed a rather low reproductive effort. However, the mean seed output per plant was 34.8±16.8 and the productivity appeared very constant every season. Thus, in the natural populations young plants are borne and recruited every season by means of sexual reproduction. A. monanthum was found to be characterized by annual type dry matter economy. The sexuality and reproductive systems of this species turned out to be extremely complex, and ten different reproductive types were distinguished. The exceedingly low efficiency of sexual reproduction in this species is apparently supplemented by vegetative propagation. The dry matter allocation to daughter bulbs at final harvest was very high; whereas the allocation to sexual reproduction was extremely low. InA. Grayi (a polyploid complex of 4X, 5X, and 6X), a surprisingly high amount of the total annual net assimilate is allocated to the bulbils and bulblets. On the other hand, sexual reproductive effort in this species is exceedingly low, even in obligate amphimictic plants. Thus, the recruitment of individuals in a population of this species appears to be largely dependent on vegetative reproduction. Considering the number of bulbils produced in the scape heads, their dispersibility, germinability, and rapid growth after sprouting, the bulbils evidently possess a function almost comparable to seeds. This species no doubt possesses an adapative strategy to unstable, open habitats exposed to frequent disturbances. It is concluded that the life history strategies of plants, as characterized here in this paper for three wildAllium species, have doubtlessly differentiated by adapting to the respective ecological backgrounds of their habitats.     

The productive and reproductive biology of flowering plants

Summary The seasonal growth cycles and dry matter partitioning of Heloniopsis orientalis (Thunb.) C. Tanaka (Liliaceae) into its component organs throughout the year were studied and compared with one another in five selected populations at different altitudes in Toyama Prefecture, Japan (i.e., 100, 200, 900, 1,900, and 2,600 m above sea level). In addition, reproductive energy allociation (RA) and reproductive capacities of these five populations were critically analyzed in relation to environmental factors of each habitat.As a result, a remarkable cline in the growth cycle, dry matter allocation as well as significant reproductive characteristics including reproductive capacity and allocation was discovered along the environmental gradients (e.g., the length of the growing season) present as a result of different elevations. There is a clear negative correlation between the reproductive capacities and allocations in these five populations (r=0.9236, P<0.05), i.e., the populations of H. orientalis allocate increasingly greater energy to reproductive activities in response to the increase in elevation, but, on the contrary, show a marked decreasing tendency in reproductive capacity. Likewise, there is a tendency not only of increased energy allocation to total reproductive structures, but also toward producing a single propagule in successively harsher habitats. Specifically, the RA to total reproductive structures at the fruiting stage incrases from 9.97%, 13.03%, 15.25%, 23.06% to 25.52%, and also the relative amount of the energy invested to producing a single propagule increases from 1.000, 1.298, 2.496, 5.512 to 6.079 in response to an increase in elevation.